In the manufacture of ophthalmic lenses, it is often necessary to apply an adhesive film on the surface of a lens in order to protect the lens against scratching or against chemical attack by foreign bodies, e.g. during "blocking", i.e. when a metal block is fixed on one face of the lens by casting a low melting point metal onto the lens for the purpose of subsequently mounting the lens on the holder of a surfacing machine, an edging machine, or a polishing machine. It is particularly recommended that such an adhesive protective film be applied on lenses made of an organic material, however such a film may also be applied to lenses made of glass.
In order to apply an adhesive film on a face of a lens, one prior method consists in placing the lens in an upwardly open cavity on a support capable of being moved vertically within the cavity under the control of an actuator. An adhesive tape is then brought manually over the cavity in which the lens is located, thereby closing the cavity. An annular jaw is then manually displaced to keep the adhesive tape pressed against the edge of the opening to the cavity. The lens support is then moved vertically upwardly under the control of the actuator, thereby applying the adhesive tape to the top face of the lens, optionally with the assistance of a vacuum if the cavity is connected to a vacuum pump. The adhesive tape is then manually cut by the operator around the lens by means of a cutting implement or "cutter". The jaw is then manually opened and the lens is manually removed together with the disk of adhesive film stuck to its top face. All, or nearly all of the above-mentioned operations are manual and therefore take place relatively slowly. Further, given that the adhesive tape is initially flat and that the face of the lens that needs protection is generally a curved surface, it is generally not possible to avoid forming folds when the adhesive tape is applied to the face of the lens, in particular when the said face of the lens is highly curved (i.e. has a small radius of curvature). These folds prevent the adhesive tape from adherring properly to the face of the lens and make it impossible to obtain a layer of uniform thickness between the lens and the metal block which is subsequently cast onto the adhesive film.
The object of the present invention is therefore to provide a method and an apparatus for applying a protective film on one face of a series of ophthalmic lenses at a considerably higher rate than has been possible in the prior art.
A subsidiary object of the present invention is to provide an apparatus of the above-mentioned type in which the protective film is applied against the face of the lens without folds being formed, even if the lens has a small radius of curvature.
Another subsidiary object of the invention is to provide an apparatus of the above-mentioned type, capable of applying the protective film over the entire face of the lens to be protected regardless of the diameter of said lens.